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How to unblock a sink

Dealing with blocked sinks

UPDATE: Because the world and his wife seems to have gone crazy for Soda Crystals and White Vinegar since Mrs Hinch recommended them for cleaning sinks, we're encouraging customers to read this article and particularly the paragraph at the end of this page about mixing acids and alkalis. So in the meantime, a bit of background:

Most blockages in sinks are the results of grease and oil congealing in the pipes as the waste water cools. The build up can also trap food debris, further restricting the flow of water through the pipe. Bacteria can grow on this, giving the resultant bad odours.

If neglected, this can cause a total blockage. It's best to tackle the issue as soon as you notice water draining more slowly. Or even better, to prevent it happening in the first place.

Tackling a blocked or slow draining sink

BLOCKED SINKS - Remember, prevention is better than cure! Once a pipe is totally blocked, your best options are plunging and rodding, but Soda Crystals might sort the problem. It's certainly worth trying.

We don't like to recommend toxic products like caustic soda (not to be confused with Soda Crystals) because of the health & safety implications. If you do resort to such measures, please ensure you use gloves and safety goggles and limit the amount of skin exposed that could be affected by splashes. 

SLOW DRAINING SINKS - In all but the worst blockages, Soda Crystals will remove a 'normal' blockage. Simply pour some boiling water down the sink; once it has all but drained away (albeit slowly), pour in a mug of Soda Crystals. Then add another mugful of boiling water and leave for 5 mins. Then pour in a kettle full of boiling water to see if the issue is resolved. If it isn't repeat the process until the drain flows freely. All being well, you should see the drain rate improve with each treatment.

If the blockage is particularly bad, you could try bicarbonate of soda and white vinegar prior to the Soda Crystals treatment. By pouring bicarbonate of soda (or Soda Crystals) down the drain, followed by white vinegar, the resulting chemical reaction could dislodge some of the debris by agitation.

AVOIDING THE PROBLEM IN THE FIRST PLACE - Simply put a mugful of Soda Crystals and hot water down your drains each week and you shouldn't have a problem. They are biodegradable and can even be used in houses with septic tanks. There are other things you can be doing to prevent a blocked drain.


NB. Do not use soda crystals or liquid soda crystals on aluminium or lacquered surfaces.

Pipe blocked by grease

Photo courtesy of Northumbrian Water

Pouring Soda

Sink cleaning

What about bicarb (or Soda Crystals) and white vinegar?

You may well have seen plenty of 'how to' videos on the internet about unblocking sink plug holes and drains. One of the (visually) more interesting tips is to pour bicarbonate of soda or baking soda  (or Soda Crystals) down the plug hole and then add white vinegar and watch the fizzing fun begin! You may also remember from chemistry class that bicarb is alkali and vinegar is acid. So the reaction you are seeing is the two effectively neutralising each other. So is it actually helping?

The answer in a roundabout way is 'yes'. But......there's a much better solution. Our MD (and qualified chemist) Bruce Maxwell explains:

"Adding vinegar and bicarb will fizz like crazy and the physical action will knock around debris.  The bubbles will do a bit of cleaning, but bicarb is not a great cleaner for sink drains as its pH is too low – it would be better to use a stronger alkali such as Soda Crystals with hot water. This will react with any fats and oils that are restricting the pipe, and make them water soluble, and flush away with the other matter that is causing odours and/or restricted flow. Adding vinegar after a good soak in Soda Crystals will fizz and make sure everything is knocked off the pipe walls."

45 thoughts on “How to unblock a sink

    1. Follow the dosage for ‘strong solution’ as detailed on the side of the bag. In practice, it may be easier to simply tip about a mugful down with some very hot water, about once a week.

  1. Hi, my kitchen sink is not necessarily blocked and in general is kept clean with bleach, however, when the washing machine is in use some awful smells come up through the plughole, very stinky air!!!
    I have bought some of your crystals, where shall I start??

    1. Bleach kills germs but it doesn’t dissolve grease…so it’s only a temporary fix. Bacteria will soon grow back on the debris in the pipes. You’d be much better switching to a regular dose of soda crystals down the drains and in the washing machine. Here’s the advice for washing machines.

  2. Do Soda Crystals dissolve hair and soap build up in bathroom drains? I have three daughters with long hair and it’s always clogging up the drains!

    1. Soda Crystals won’t dissolve hair…that’s why it’s very safe to use. It WILL dissolve the oil and residue shampoos that will cause it to clump. Caustic soda WILL dissolve it, but be very careful when using it. Prevention is better than cure ie use Soda Crystals regularly to stop greasy build up and use a strainer/trap. The shower unit should have one anyway. Every few days, remove the trap and pull out the hairs.

  3. Hi. You answered a question last year about using your product to clean the system on a jacuzzi bath. But what ratio crystals to water and does it matter how hot the water is?

    1. Hi Keith – there isn’t really a ratio. Using bath hot water add a bag and see what the effect is. You may want to seek specialist advice, but the principles of using Soda Crystals are the same as using a washing machine. It will help clear dirt and gunk and in particular oily residue build up. Not that we expect there to be, but Soda Crystals shouldn’t be used on aluminium, zinc or copper. It’s always better to keep adding more crystals than adding too much, mainly because you’re just wasting them.

  4. Hi,
    We’ve got a problem with the smell of dog urine on our artificial grass and there is some mention online of using soda and white vinegar to get rid of the urine crystals that build up under the plastic grass. I’m confused over which ‘soda’ is meant – is it Soda crystals? – and have you got any recommendations and explanation as to how it works. Just so we can get the best results. Thanks !

    1. Hi Jeremy – we don’t have particular knowledge of artificial turf, but it sounds like the advice is based on neutralising the acidity of the urine, which alkali Soda Crystals will do. This is our general advice on tackling pet accidents. Bicarb could be useful in this instance as it is also alkali but has better odour removal properties than Soda Crystals.

  5. Can soda crystals be used for hot tub ph balancing? The one we buy from our hot tub supplier is labelled “contains sodium carbonate” We pay about £8.99 for a 1.5kg tub so would love to find out if a saving could be made here

    1. Hi Ian – yes you can. You need to use at a ratio of 1:2.7. So if you normally use 1.5kg, you’d use 4.05kg of Soda Crystals. So yes, you WOULD save money using Soda Crystals.

  6. Paul thanks for the reply. I understand I need to use soda crystals and hot water, but do I flush the loo? I am not sure on that point. I assume it will all be flushed away, but I want to clean the pipes, not necessarily the loo itself. I am planning a major clean, so plan to use a few cups with a few buckets of hot water. Maybe I don’t need to flush, since the water will drain away? You advice is very welcome! I am just not sure how it happens.

    1. Hi Dotty – the need to clean toilet pipes is somewhat different to sinks and drains; principally that they aren’t subject to the same build up of greasy deposits, which can cause blockages. If toilets get blocked, it’s often to do with too much toilet roll being used or other objects that shouldn’t have been discarded in the loo. The aim is to clean the bowl. The combination of (very) hot water, the cleaning and water softening properties of the soda crystals combined with the natural abrasion (from the crystals and the brush) is sufficient to clean a standard toilet bowl. By all means let the Soda Crystals solution sit for a while before flushing.

    1. Hi – have you read the article? The message is that prevention is better than cure. If you’ve got a TOTAL blockage that Soda Crystals or a plunger aren’t sorting then you’ll have to resort to harsh chemicals (make sure you follow the health & safety guidance), rods, or a plumber.

      You may want to read the comment from Glenn Miller at the bottom of this page.

  7. What is the best way to use soda crystals in a wash-hand basin with a spring-loaded pop-up plug which doesn’t seem to be removable?

    1. Dissolve the Soda Crystals in hot water and fill the sink. They open the plug hole and let the solution drain. If it drains very slowly, you have an obstruction. Either try plunging after the solution has drained or repeat the process until water drains freely.

      Then run the hot water tap for 30 seconds or so until the sink drains.

    2. I have two wash-hand basins with spring-loaded pop-up plugs and remove them by unscrewing/turning them around. Simple but it also took me a while to work it out!

  8. There is a same problem here, but water is accumulated in the kitchen sink and don’t move. Is this a wise solution to use baking soda/vinegar or soda crystals/hot water?

    1. If the water simply isn’t moving, a plunger should normally clear the blockage. Remember to block the overflow hole before plunging. Once the water is starting to drain, follow the instructions using Soda Crystals and hot water.

  9. Is it safe to pour soda crystals down the kitchen sink followed by a kettle full of boiling water, or could it damage the plastic pipes and joints? Thanks for your assistance.

    1. Hi Susan – yes it’s fine. The water will start to cool as soon as it hits the sink and drains. Soda crystals and very hot water are ideal for dissolving grease. Use boiling water and then after a minute run the hot tap for a minute so that all greasy residue is sluiced down the pipes to the main sewer system. HOWEVER, do try to remove as much solid fat from pans before washing them. Otherwise sewerage systems themselves can get blocked. Many water companies will give you a free fat trap, so that you put less fat down the drains.

    1. In theory, you certainly can, but in practice it will have limited benefit for cleaning. The acid and alkali are simply reacting with each other and neutralising.

  10. Hi,, we have a spa bath and wondering if it would be possible to use soda crystals to clean the system? Thanks ms in advance

    1. Yes – they are ideal. Just check with the manual or manufacturer that there are no aluminium, zinc or copper components to be safe (which there shouldn’t be).

      You can now get 1.5kg bags from Wilko (own brand) and Waitrose (DP brand) for heavier use applications like this.



  11. I am wondering if there was a way to use bi carb to keep the water in a hot tub clean rather than chemicals.

    1. Hi Annie – Soda Crystals would be better for cleaning (assuming there are no aluminium, zinc or copper parts) but it would be advisable to check with the hot tub manufacturer.

  12. Can I use soda crystals to clean the bathroom basin waste and shower waste as I have a Saniflo pump system and the pipes occasionally get blocked with accumulated hair and soaps/ conditioner?

    1. Hi Sue – yes they’re fine. The only metals Soda Crystals shouldn’t be used with are aluminium, zinc and copper/

  13. Can I use Soda Crystals to degrease my dishwasher, branded cleaners are expensive and I have not found them very effective.

  14. Are soda crystals safe to use with a septic tank / cess pit? We have to be really careful what we use but I can’t seem to find out if soda crystals would be a option.

  15. my bathroom sink is really blocked. how much soda crystals should i use and how long should i leave them before adding vinegar and then flushing with hot water?

    1. Is the water draining but slowly? If it’s not even draining, then it may be totally blocked and plunging should be your first action. Remember to block the overflow drain hole with a cloth and hold it in place. Get someone else to help if needed.

      If it is draining, albeit slowly, try putting half a bag of Soda Crystals into the basin with just enough boiling water to wet all the crystals. Leave to slowly sink down the hole, adding more small amounts of boiling water as needed to keep them going down the hole. Once the speed of draining increases, keep putting some more boiling water and Soda Crystals down the sink until the blockage has been removed and the material moved away to the main sewer.

      The use Soda Crystals regularly to prevent it happening again.

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